1. Field of the Invention
The present invention relates to a barrier device for a camera, and more particularly, to a barrier device disposed in front of a taking lens of a camera lens barrel.
2. Description of the Related Art
In recent years, cameras have been highly automated and made compact to improve user-friendliness and functionality. Among these, some camera has a barrier device mounted in front of a taking lens of a lens barrel. Most of barrier devices include barrier blades automatically closed when the lens barrel is put into a retracted state in conjunction with operation of a zoom mechanism or a retraction mechanism.
With the progress of downsizing of camera, the lens barrel is made small in diameter, making it difficult for the barrier device with two blade members to fully cover the lens of the lens barrel. To obviate this, there has been used a barrier device with four blade members to cover the lens. The four blade members overlap one another for compact accommodation in a space of small area when the photographing opening (lens opening) is open.
Some conventional barrier device with four blade members includes barrier members openably/closably attached in front of the taking lens and a barrier drive means for opening/closing the barrier members (see, for example, Japanese Laid-open Patent Publication No. 2001-083575). The barrier members consist of two pairs of a large main blade member and a small auxiliary blade member, which are opened/closed on the same plane extending nearly perpendicular to the optical axis of the taking lens. Each auxiliary blade member is opened/closed to follow the motion of the corresponding main blade member. The barrier device further includes, as a part of the barrier drive means, spring members interposed between corresponding ones of the main and auxiliary blade members and urging them in an opening or closing direction.
Another conventional lens barrier device includes two sets of first and second barrier blades respectively pivotably supported at symmetrical positions on a ring-shaped barrier cover, springs each applying a closing force to the corresponding set of barrier blades, and cams respectively disposed at symmetrical positions on a barrier drive ring and each adapted to drive a drive pin for the corresponding set of barrier blades. Thus, the four barrier blades are independently driven to open and close on the same plane (see, for example, Japanese Laid-open Patent Publication No. 2002-148682).
The above conventional barrier devices with four blade members are configured to open/close two pairs of main and auxiliary blade members by the barrier drive means and urge the blade members in a closing direction by the spring members each disposed between the corresponding pair of blade members.
Thus, the main and auxiliary blades are held in a closed state by being urged in the barrier closing direction by the springs and put into an open state by being applied with a driving force in the barrier opening direction against the urging force of the springs.
In the conventional barrier devices with four blade members, therefore, the driving force to drive the blade members in the opening direction must be made stronger than that to drive them in the closing direction.
The two main blade members must be retained in closed positions when the four blade members are in the closed state, even if a foreign matter is pinched or if a sudden operation is made by a user. Thus, the urging force to close the main blade members must be made large.
As a consequence, especially in the barrier device with four blade members, both the drive forces acting in the blade opening and closing directions must be made strong, resulting in a fear that drive loads on the blade members become large and barrier component parts are twisted to cause an operation failure when the barrier is opened/closed.